Optical fiber communications systems are becoming increasingly important in the high speed transmission of large amounts of information. A typical fiber communications systems comprises a source of optical input signals, a length of optical fiber coupled to the source, and a receiver for optical signals coupled to the fiber. In essence, an optical fiber is a small diameter waveguide characterized by a core with a first index of refraction surrounded by a cladding having a second (lower) index of refraction. Light rays which impinge upon the core at an angle less than a critical acceptance angle undergo total internal reflection within the fiber core. These rays are transmitted with minimum attenuation in guided modes along the axis of the fiber.
Optical filters are used for shaping the spectral features of transmitted optical pulses, and multiplexers are used for transmitting a multiplicity of different signals at different wavelengths. The present invention relates to devices which can be used as filters and as demultiplexers to separate multiplexed signals in optical communications systems.